Distortion-measuring system



G. s. VERNAM ET AL DISTORTION MEASURING SYSTEM YFiled My 25, 1923 Q r v Mw N n Y Us@ sept'. 29, 1925'.

Patented Sept. 29, 1925.

UNITED STATES PATEIW OFFICE.

GILBERT S. VERNAM, 0F BROOKLYN, NEW YORK, DONALD B. PERRY, OFiMAPLEWOOD, NEW JERSEY, AND SAMUEL I. CORY, OF ELMHURST, NEW YORK, ASSIGNORS TO AMERICAN TELEPHONE AND TELEGRAPI-I COMPANY, A CORPORATION OF NEW Yong.

DISTORTION-MEASURING SYSTEM.

Application :filedA May 25, 1923. Serial No. 641,452.

To all whom t may concern.'

Be it known that we, GILBERT S. VERNAM, DONALD B. PERRY, and SAMUEL I. CORY, residing at Brooklyn, Maplewood, and Elm.- hurst, in the counties of Kings, Essex, and Queens and States of New York, New Jersey, and New York, respectively, have invented certain Improvements in Distortion- Measuring Systems, of which the following is a specification.

This invention relates to electrical measuring systems and particularly to means fo'r determining the existence and magnitude of distortion of telegraph signaling impulses f produced in the co-urse of transmitting the said impulses.

In transmitting telegraph signals, each made up of a plurality of impulses andeach impulse having a definite length, distortion of the impulses and therefore of the signais may be produced by' various causes inherent in the line or in the apparatus connected therewith or both. The distortion with which this invention is concerned manifests itself in lengthening or shortening the duration of the impulses which constitute the signal transmitted over the line. This lengthening or shortening of the duration of the impulses interferes with the proper recording of the signals at any station connected with the said line and consequently impairs the eciency of transmission.

Various systems for determining the existence and magnitude of this form of distortion have been devised and used, but due 4either to the complexity of the apparatus required or to other causes such use has not been very wide. One such method consists in the use of a Vheatstone tape recorder connected with the receiving end of a line to which perfect signals are applied at the sending end for the purpose of recording the said signals at the receiving end. Thetape records of these signals are then measured whereby Vany distortion and the magnitude thereof may be determined. This method, however, is quite laborious and is unsatisfactory in other ways.

It is the object of this invention to provide means for the measurement of telegraph distortion of the character heretofore described which would not only be portable but also give directly the complete results of such measurements.

This invention will be clearly understood from the following description when read which Figure l shows one form of embodiment of the invention, and Fig. 1a is a graph used in describing Fig. 1.

In Fig. l there is disclosed below the line AAthe transmitting apparatus by means of which telegraph signals may be applied to the line Ll which extends to some distant point and is there looped back to the same station from which the signals were transmitted and are received by the receiving apparatus shown in Fig. l above the line AA. That is to say, in the form we have chosen to disclose cur invention the transmitting and receiving apparatus are located at the same station and the circuit is so connected at some distant office that the trans mitted signals are received at the same sta! tion from which they are sent. It is to be understood, however, that the invention is 'by no means limited to the making of distortion measurements upc-n looped circuits `in connection with the attached drawing of but is also adapted for the measurement of y distortion over what may be termed straightway circuits where the transmitting and receiving apparatus are in different offices. The invention may also be used in measuring the distortion produced by ap-pa ratus per se or by lines containing apparatus such as repeaters.

The transmitting apparatus which as stated is shown in Fig. l below the line AA', comprises a tape transmitter Tl which may be of any well known type comprising a plurality of movable contact levers designated l to 5 inclusive. These levers are controlled by the perforated tape through certain selecting pins (not shown) which serve to cause the Contact levers tf) take a position against one or the other of the busbars 6 or 7, the relative position depending upon the presence o-r absence of a perforated hole in the tape above the selecting pin of a particular contact lever. rPhe levers 1 to are connected with the segments S, to S5 respectively` of the segmental distributing ring D1. The stepping magnet Ml of the tape transmitter T1, by means of which the soV the movable contact springs of the keys K1 to K, inclusive. The fixed contacts of these keys Vare connected with the conductors 8 and 9 with which are also connected the busbars G and 7 respectively. The-conductors 8 and 9 are adapted to be connected with the tip contact ot' the plug P1 by means of the re versing switch 11. The sleeve contact of the plug P1 is connected with the ring D2 which is adapted to be connected by means of the brush 12 with the various segments of the ring D1. The ring Dl1 which is adapted to be effectively connected with the segment S12 of the ring D3 by means of the brush 13, has connected therewith a source of potential B1, the purpose of which will clearly appear later. The brush 12 is preferably fixedly connected with the brush 13 but electrically insulated therefrom so that both brushes will at any instant be in the same angular position with respect to the distributing rings.

The plug P1 is adapted to be inserted in the ack J1, the tip contact of which is connected with the transmitting relay 16.

Sources ot potential of opposite polarity 1 designated Bo and B,3 are connected with the relay 16 and with the sleeve contact of .the jack J1. It will be seen fromthe foregoing description of the apparatus comprised within the transmitter per se, that when the reversing switch 11 is upon either of' its contacts and the contact levers 1 to 5 inclusive are touching either of the busbars 6 or 7, depending upon the signal character represented by the perorations ot the tape which may be in engagement with the pins of the transmitter at that instant, that the relay 16 will be energized by current impulses as the brush 12 travels over the successive segments S1 to S5; and by the operation of the armature of the relay 1G between the contacts thereof similar current impulses will be applied to the bridge arms of the duplex terminal apparatus designated X1. The terminal circuit embraces apparatus of well known types and needs no detailed description here. The line L1 may be assumed to extend to a distant station Y where it is looped back to the station X and is there connected with the terminal circuit X2 which circuit may be similar to X1. The polar receiving relay 17 of this terminal circuit has its armature connected with the battery B1 and one of itsA contacts is connected with the tip contact of the jack J2 of which the sleeve is connected with the battery B5. This jack is intended to cooperate with the plug P2 by means of which the receiving apparatus `for the measurement of distortion may be connected elfectively with the line L1. This plug is connected through the reversing key KG with one of the windings of the line relay 18, the other winding of which is connected with a source of pofor the actuation of the magnet N2 it has been rendered possible to avoid the use of an extra segment similar to S12 of the transmitting apparatus. It in the receiving apparatus such a segment as S12 be used for -the Aoperation of M2, then the segment R6 'may be connected withy the upper contact spring of the key K1. 1t is desirable to point out that if the receiving apparatus is used ata different station 'from that at which the transmitting apparatus is located, separate kkeys corresponding to K1 to K5, inclusive, would be necessary at the transmitting and receiving stations. The segmentsy of the ring- D1 are effectively connected with the grounded common segment R11 v of the ring D7 by means of the brush 15.

The contacts of the line relay 18 are connected with the contact points of the reversing switch 19, the movable arms of which are connected with the busbars 27 and 28 of the tape transmitter T2. The armature of the relay 18 is connected through one of the windings of the relay 20 with the shortened segments R1 to R10 inclusive, of the distributing ring D5.' The relay 20, when en-V ergized, operates a visual or audible signal 26 by means of which the presence of distortion ot' the received signals is made known. lVliile the relay 2O and a visual signal 26 have been shown for the purpose oil describing this invention, other forins oi indicating devices may be used such as message registers 4or a telegraph sounder. ySegments of the ring D5 are eiiectively connected with the common segment R11 of the ring DG which is connected with a source of potential B1. This saine source is also connected by a conductor 27 with the rightliand armature of relay 20 by means of which the said relay may be locked up after initial energization. A release key is included in the locking circuit of relay 2O to lfacilitate the restoration to normal of the said rela-y aiter it has locked up. All of the brushes of the distributing rings D1 to DS inclusive, are operated in synchronism, which, if the transmitting and receiving apparatus are at the same station, may be done by connectingk all of said brushes to the same driving shaft. If the transmitting and receiving apparatus are at different stations, some form of synchronous driving apparatus such, for example, asthe well known phonic wheel motor7 may be used. Although the brushes of the various rings are operated in synchronism they would not under ordinary conditions be in phase each with the others, because of the time lag between the transmission and reception of the signaling impulses, which will be made clear hereinafter.

The manner in which the aforedescribed system functions in order to measure the distortion of the signaling impulses transmitted over a line is as follows:

Let us assume that by means of the irst live segments of the ring D1 there will be applied to the line Ll for each revolution of the said ring, a signal character which will be determined by the perforations of the tape which controls the transmitter T1. And, furthermore7 it will be assumed that by meansof the last live segments designated SG `to S10 of the said ring, therey will be applied to the line L1 a delinite signal character depending upon the operation of the keys K1 to K5 inclusive. If, for eX- ample, the first signal character to be transmitted over the line is such as is shown in Fig. 12L comprising alternate marking and spacing impulses, the levers of the transmitter T1 will be so actuated that the first, third and fifth will make contact with the busbar 6 and the second and fourth with the busbar 7. Assuming that the switch 11 is in the position shown in the ligure, current will flow from the battery B3 over the sleeve contacts of jack J1 and plug P1, through the brush 12 connecting 4segments Si, and S1, thence through the contact between the lever 1 and the busbar 6, over the conductor 10 `and through the winding of relay 16 to the `battery B2 which is of opposite polarity to B3. Relay 16 will be energized thereby and its armature Vwill be brought in contact with the marking battery whereby an impulse will-be transmitted over the line L1 which will be Sustained throughout thetime necessary forv the brush 12 to traverse the segment S1. This impulse will energize the relay 17 of the terminal station X2 so that current will flow from the battery BsL through the upper contact of relay 17 through the tip contacts of the jack J2 and the plug P2 and through the left-hand winding of the relay 18,thence `to the battery B5 which is of oppositepolarity to B4. Thearmature of the relay 18 will be moved from its left-hand contact where it is normally held by the energizamitter T1 do with respect to the busbars 7 and 6, because the tape of the transmitter T2 has the same signalcharacters as the tape of the transmitter T1 and the two ktransmitters are 4operated in synchronism,

but suitably adjusted for the time lag in the transmission of the signaling impulses from T1 to T2.

If we assume that the receiving rings D,i to D8 inclusive have been properly adjusted to compensate for the time lag between theV transmission and the reception of signals, the brushes 111 and 15 will make contact with the segments R1 and Ril when the corresponding undistorted signal impulse operates the line relay 18. `With no distortion and with the rings properly adjusted to compensate for the time lag in the transmission of signals, the relay 2O will not be operated when the brushes 14 and 15 make contact with the segments R, kand R1 because the said circuit which includes the source B7 will be open by virtue of the fact that the lever 21 is in contact with the left-hand busbar 28 and the armature of relay 18 is against its right-hand contact. i

In similar manner when a spacing impulse is transmitted over the line L1 the armature of the relay 18 at the receiving station will be moved to its left-hand contact. The transmittal of this spacing impulse, which is the second impulse of the transmitted sig nalcharacter, is controlled by the position of the contact lever 2 and by the traversing of the segment S2 by the brush 12. Since the Contact lever 22 of the transmitter lever T2 occupies t-he same relative position' with respect to its busbars as the lever 2 of the transmitter T1 does with respect to itsbus# bars, the circuit through the relay will be open when the brushes 14 and 15v begin to traverse the segments R2 and R2 respective` ly. This result follows because during the reception of the spacing impulse the armature of the relay 18 is touching its lefthand contact which is connected with the .busbar 28, while at this time the contact lever 22 is touching the right-hand busbar 27 sol that the circuit which includes the source B7 and the relay 20 will be open at the contact lever. As the brush 12 moves over the segments S3, S4 and S5 of the ring D1 impulses corresponding to the relative positions of the levers 3, 4 and 5 will be transmitted over the line L1. These impulses will operate the line relay `18 and `if there of the brush'12 thereover. sage of the brush 12 onto the segment Su is no distortion of the said impulses the relay 20 will remain unoperated during the movement of the brushes 14,- and 15 over their respective segments. 1

` After the signal represented by the impulses set up on the segments S1 to S5 inclusive, has been transmitted, the signal set up on the segments SG to S10 inclusive, will then be transmitted by the movement With the pasthe brush 13 which moves in phase with the brush 12 passes onto the segment S12, thereby connecting segments S12 and S12 and permitting current to flow from the battery B1 through the winding of the magnet M1 which steps ahead the tape of the transmitter T1 so as to control the position of the cam levers 1 to 5 inclusive, in accordance with the new signal character represented by that position of the tape. It will be seen therefore, that the transmitter T1 is in a position to transmit the next signal character over the line L1, but it does not do so until the brush 12 has traversed segments S6 to S10. The signal character set up upon the latter group ot segments is controlled by the operation of the keys K1 to K5 inclusive. lith the keys in the position shown in the ligure and with the switch 11 also in the position shown, the circuit of the relay 16 will be open at the key K1 when the brush 12 traverses the segment SG, thereby allowing the armature of the relay 16 to fall back and impress a spacing signal upon the line L1. As the brush 12 traverses the segments S7 to S1o inclusive, there will be impressed upon the line L1 alternate marking and spacing impulses with the keys K2 to K5 in the position shown. At the receiving end of the line the magnet of the transmitter T2 would be operated when the brush 15 passed. on-

to the segment RG and the tape would be stepped ahead in synchronism with the movement of the tape of the'transmitter T1. The impulse transmitted over the line by the passage of the brush 12 over the segment- S6, would be received at the distant end of the line and the line relay would be actuated, but in view of the fact that the segment R6 has been utilized for the operation of the magnet M2 and the corresponding segment R6 of the ring D5 has been left open, no indication of distortion of this impulse will be given by the receiving apparatus. This imposes no serious limitation upon the efficiency of this method of distortion measurement and, as has been pointed out heretofore, this impulse may be received and its distortion determined if a separate segment be inserted at the receiving end of the line corresponding to the segment S12, such segment being connected with and intended to control the magnet M2.

In order tomeasure distortion kthe receiving apparatusshould be calibrated during the reception of undistorted signals. In making loop tests wherein the transmitting` apparatus is at the same station as the receiving apparatus, it is a simple matter to connect the two apparatuses directly together so that undistorted signals will be impressed upon the receiving apparatus. In making straightway tests where the receiving apparatus is at a different station Jrom the transmitting apparatus, it may be necessary to have at the receiving station a separate source of undistorted signals. The rings D5 to DS inclusive are preferably arranged so that they may be orientedrelative to the brush driving-shaft. l/Vhile the undistorted signals are actuating the line relay 18 the said rings should be oriented together, rst in one direction until the point is reached where they are so far out of phase with the incoming signals as to cause the operation of the signal 26. Upon the closing` of the left-hand contact of relay 20, the signal 26 is operated which indicates that the orientation has been sufficient as to producevfailure in the reception oi signaling impulses. The closing of the right-hand contact energizes the locking winding of the relay which thereafter remains locked until released by the operation of the release key. The operation of the relay 2O results from the simultaneous connection of the contact lever of the tape transmitter and of the armature of the line relay with the same busbar. As heretofore pointed out, when an undistorted impulse is received, the armature and the contact lever of the transmitter T2 corresponding to that impulse are at the same instant of time connected with different busbars. AThe movement of the rings D5 to D2 simply means that the synchronism existing between the operation of the line relay and the passage of the brushes over the corresponding contacts of the various distributing rings has been destroyed. The distance through which the rings D5 and D8 may be oriented while receiving undistorted signals before failure takes place, is known as the margin. When the margin has been obtained for orientation of the rings in one direction, the rings are then oriented in the 'opposite direction until failure is evidenced bythe operation of the signal 26, and the margin in that direction is thus obtained.

With the apparatus thus calibrated, that is to say, having determined the margin for undistorted signals the neXt step is to adjust the receiving apparatus for time lag. Signals should be transmittedA over the line and the rings D5 and D8 should be oriented that the brushes 14 and 15 will make contact with segments `R1 and R1 when the corresponding impulse operates line relay 18. Having the apparatus calibrated and adjusted for time lag, the next step is to measure the distortion of signals.

If the signals received over the line Ll by the relay 18 are distorted, that is to say, a certain impulse may be lengthened and its .adjacent impulse or impulses may be shortened, such distortion manifests itself in the diminution of the margin through which the rings l)5 and DS may be oriented. l/Vith undistorted signals it should be possible to orient the ring D5 to such an extent that undistorted signals would be properly received throughout a range extending from a point approximately midway between R, and the preceding segment R10 to a point approximately midway between R, and the succeeding segment R2. As distortion increases, this margin is diminished and the magnitude of the distortion may be represented by a fraction whose numerator is the difference between the margins for undistorted and distorted signals and whose denominator is the margin when the signals lare undistorted.

It will be seen, therefore, that by means of the system disclosed herein the magnitude of distortion of telegraph signaling impulses, may be efficiently determined. It is also desired to point out that by using a tape transmitter a great variety of signal combinations may be impressed upon and transmitted over the line so that the tendency of the line and its associated apparatus to distort signals may be studied to determine its effect upon signals having different impulse combinations. This is an important characteristic of the invention disclosed herein because it is well known to those skilled in the art, that a certain line may transmit, without appreciable distortion, a signal or signals having certain combinations of impulses but would tend to distort greatly signaling characters having diiferent combinations of impulses.

While this invention has been disclosed in a particular form and arrangement of parts, it is not so limited but is capable of embodiment in other and different forms within the spirit and scope of the appended claims.

What is claimed is:

1. In a distortion measuring system, the combination with an electrical network capable of producing distortion of current impulses transmitted therethrough of signal transmitting means adapted to apply a succession of different signals to said network and signal receiving means also connected with said network and having means to indicate distortion of the received signal.

2. ln a distortion measuring system, the combination with an electrical network capable of producing distortion ot' current impulses transmitted therethrough of a source of signaling impulses connected, with said network and having means for changing the successive signals in a predetermined manner and signal receiving means also connected with said network and having means to indicate distortion of the received signals.

8. In a distortion measuring system, the combination with an electrical network capable of producing distortion of current impulses transmitted therethrough of signal transmitting means connectedy therewith, the said transmitting means having a device 1 for changing in a predetermined manner the successive signals applied by said transmitting means tov said network, and signal receiving means adapted to indicate distortion and to measure the magnitude thereof.

4i. In a distortion measuring system, the combination with an electrical transmission system capable of producing distortion of current impulses transmitted therethrough of signal transmitting means connected with said transmission system and having means for changing in a predetermined manner the successive signals applied to said transmission system, and signal receiving means adapted to indicate distortion and to measure the magnitude thereof.

5. In a distortion measuring system, the combination with an electrical transmission system of a tape controlled signal-transmitting means, and a tape controlled signalreceiving means having a device connected therewith to indicate distortion of the received signal.

6- In a distortion measuring system, the combination withan electrical transmission system of a printing telegraph transmitting station connected with the said system comprising a tape transmitter, a distributor for applying the signaling impulses to the said line and a printing telegraph receiving station connected with the said system comprising a tape controlled receiving device, a plurality of distributors and means to indicate the distortion of the received signals set up on the said distributors.

7. In a distortion measuring system, the combinationwith a line of a printing telegraph transmitting station connected with t-he said line comprising a tape transmitter and distributors for applying the signaling impulses to the said line, a printing telegraph receiving station connected with the said line comprising a tape controlled receiving device, and a plurality of distributors, means to indicate the distortion of the received signal, and means to synchronize the operation of the distributors at the transmitting and receiving stations.

8. ln a distortion measuring system, the combination with a line of signal-transmitting means comprising a tape controlled transmitter and also a source of fixed signals, and signal-receiving means comprising atape controlled receiving device and a plurality of switching devices for the receptionl respectively of the signals impressed upon the said line by the said tape transmitter and the said source of fixed signals, and means to indicate the distortion of the signals received trom their source.

9. In a distortion measuring system, the combination with a line of a transmitting distributor having connected therewith a tape transmitter to set up a succession of different signals upon the said. distributor and means to set up` a fixed signal upon the said distributor whereby variable and fixed signals may be applied to the said line, and a receiving' distributor having' connected thereto a tape controlled receiving device and also a plurality of switching' means '20 whereby the said variable and fixed signals may be received and means to indicate the distortion of any of the said received signals.

l0. In a distortion measuring system, the combination With a line ot duplex terminal apparatus connected With each end thereof. tape controlled signal-transmitting means connected With the terminal apparatus at one end ot said line, tape controlled signal-l receiving means connected with the terminal apparatus at the other end of said line, the said signal-receiving means havingr connected therewith means to indicate thefdistortion of the received signal.

In testimony whereof. We have Signed our names to this specification this 24th day of May, 1923.

GILBERT S. VERNAM. t DONALD B. PERRY.

SAMUEL I.' CORY. 

